1. Field of the Invention
This invention relates in general to seat belt restraint systems used in vehicles to protect the occupant in the event of sudden decelerations. In particular, it relates to seat belt webbing adjusters used in aircraft passenger lap seat belts.
2. Description of the Prior Art
As is well known, a lap seat belt, when buckled and adjusted snugly across the waist of the passenger, holds a passenger safely within a seat during sudden decelerations of a vehicle. A typical aircraft passenger lap seat belt consists of two lengths of seat belt webbing, each anchored to the seat at one end, one webbing (here selected to be the left side length) having a buckle connector attached to its free end, and the other webbing (here selected to be the right side length) having a combined buckle and webbing adjuster attached to it so that the buckle connector fits into and releasably locks with a buckle to join the two side lengths of webbing together and form the seat belt.
The webbing adjuster includes a moveable load bar in a base frame. The free end of the right side length of webbing is inserted through a slot in the bottom of the base frame, wound around the load bar, and then passed back through the slot to exit the webbing adjuster. With no tension in the webbing, the webbing adjuster is said to be in the adjustment mode and the length of belt webbing may be adjusted by pulling on the free end of the webbing.
When the belt has been joined at the connector and buckle and the webbing adjuster adjusted, only a slight amount of tension need be applied to the webbing in order to move the load bar and place the webbing adjuster into the locking mode. Thereafter, and in order to lengthen the belt, the base frame of the adjuster must be tilted in order to release the load bar and place the webbing adjuster back into the adjustment mode. The belt may then be loosened to increase the length of the anchor end of the webbing.
Typical load bars in the prior art have a knurled cylindrical shape with integral projecting lugs on each end which allows the load bar to slide between sloping slots located in the flanges of the buckle base. The knurled cylindrical shape tends to wear and fray the webbing thus decreasing the locking reliability of the web adjuster. One assembly problem associated with such an arrangement is that the flanges on the base frame first must be spread to permit the lugs to be inserted and the flanges must then be bent back into their original shape.
Another prior art combination lap belt buckle and webbing adjuster uses a partially cylindrical bar with an axle insert that partially rotates when tension is placed on the anchored portion of the right-hand webbing. However, because the gap between the load bar and the base frame is only about 75 percent of the thickness of the webbing, as shown in FIG. 4, under normal tension the load bar does not rotate far enough to securely hold the webbing between the notch and body. When heavy loads are suddenly applied to the webbing adjuster, as in deceleration during landing or crash situations, the load bar rotates further counter-clockwise, pinching and joggling the loose webbing around the end of the bar and through a close series of very tight 90.degree. bends as shown in FIG. 5, until the webbing is clinched between the notch and the body and web lock occurs. However, moving the webbing through a series of tight bends and clinching actions in the continuous adjustments to which the belts are subjected results in excessive wear and tear on the webbing, causing it to fray and become thicker. As the webbing becomes thicker, its thickness tends to interfere with the pinching and joggling action that must take place within the close area B of FIG. 5, under load conditions. If pinching does not occur immediately as a sudden load is applied, the web lock may fail.
Other typical configurations and arrangements of seat belt adjusters seen in the prior art and in the marketplace are disclosed in U.S. Pat. No. 3,118,208, U.S. Pat. No. 3,576,056, U.S. Pat. No. 4,366,604 and U.S. Pat. No. 4,679,852.